If the club don't do one, then you might need to get a custom flag made, although you may need to ask for the club's permission to use the crest.
A quick Google finds quite a few online custom flag sites, the following is just one example (although not a recommendation as I know nothing about them).http://123flag.com/?gclid=Cj0KCQjw37...saAtqLEALw_wcB

Buy cheep England flag from supermarket. Cut seagull badge out from one of the free ones you must have from the many the club have given away. Add with a bit of wonder web. Job done. Use a tea towel in between iron and flags so not to melt it.

Buy cheep England flag from supermarket. Cut seagull badge out from one of the free ones you must have from the many the club have given away. Add with a bit of wonder web. Job done. Use a tea towel in between iron and flags so not to melt it.